1. Field of the Invention
The present invention relates to a method for the manufacture of an insulation board for a gradient coil, of the type wherein bodies that serve as spacers during the manufacture of the flow paths for the casting resin are mounted on a base.
2. Description of the Prior Art
Gradient coils for magnetic resonance imaging scanners (MRI scanners) are designed such that several coil conductor layers, which are used to generate magnetic fields, are electrically insulated from each other by interleaving insulation boards. After the assembly of the coil, the interstices inside the coil are filled with a casting resin under a vacuum. In order for the gradient coil to function as desired, all interstices must be perfectly filled, because defects such as contraction cavities, improperly impregnated spots, or air pockets may result in partial discharges or short circuits. Defects of this kind can even cause a total failure of a gradient coil. Defects must also be prevented due to the significant forces that arise during the operation of the magnetic resonance imaging scanner.
In order to facilitate the flow of the casting resin into the interstices, it has already been proposed to put a suitable spacer between the individual layers of copper coils and insulation layers in order to hold open the flow path for the filling compound in the right direction. For example, mutually interconnected plastic pins are used as such spacers. It is also possible to wind plastic strings around the coil with regular spacing between them. These plastic strings are then squeezed in order to hold open the flow path for the rising casting resin.
DE 103 15 539 A1 discloses a gradient coil in which the insulation layers have elevated spots, between which flow paths are created for the casting resin. These elevated spots can be produced, for example, by applying a reaction resin as a chain around the insulation layer, which is subsequently cured at an increased temperature. It is difficult to produce these elevated spots in such a manner so that they all have the same distance from each other. As another option, it has been proposed for the elevated spots be stamped. A disadvantage of this method is that it requires relatively expensive tools. In addition to the initial high cost, once a certain pattern of elevated spots is created it cannot be changed so that in practical application, a large number of different and costly tools would be needed.
Furthermore, DE 41 41 514 A1 discloses a gradient coil system in which U-shaped profiles are uniformly distributed as spacers in an interstice between every two shells to be insulated. These profiles are, at least approximately, as large as the distance between the shells to be insulated. The interstices filed with a casting resin then form a structure with a high shearing stiffness.